Welcome to DTP
@Katyburton
I'm sorry to hear that your dad has started mixing up night and day. Unfortunately his is very common with dementia and one of the hardest things to deal with. I've seen various suggestions on how to deal with this situation including things like giving a couple of paracetamol just before bedtime as people with dementia are not good at recognising pain but it will keep them awake. Worth a try.
I also know of at least one member who give a whisky or a hot toddy to their PWD and that has helped them sleep through the night.
Another slept during the day when her husband did.
If nothing works others have slept in a separate room and made the house safe and let their PWD wander then clear up after them in the morning. I used this technique with my dad except I was in a different house as dad lived on his own. He was always fine in the morning when I got there - usually asleep in a chair. The only thing that used to worry me was his legs were swollen as he didn't lie down with his feet up enough.
I hope these suggestions help. Has your mum got carers to help with your dad?
Looking after someone with dementia is exhausting even without being kept awake all night.